Flowers might look nice, but it turns out they can be more manipulative than we realised.

Key findings:

Both the scent and colour profiles of flowers are coordinated in the signal interpreted by bees

Combining colour and scent makes the signal for bees stronger and more stable in different environmental conditions

Researchers believe the purpose is to ensure individual bees stick to one type of plant and avoid "pollen clogging"

Scientists already knew flowers used special colours to attract the right bees, but it turns out they are also combining complex fragrances to create a combined signal.

An international team of scientists carried out a study of bees in scrubland habitat on the Greek island of Lesbos.

One of the researchers was Associate Professor Adrian Dyer, from RMIT University in Melbourne, who said flowers had evolved colours to suit bees' ultraviolet vision, but no-one understood how scent was involved.

"The team carefully investigated both the scent and colour profiles of the flowers and the very surprising thing was that the two are coordinated," he said.

"Flowers which appear blue have a certain scent profile, even if they come from different plant families."

Sending a stable signal

The team of researchers from Australia, Greece, Denmark and the United States examined the relationships between 41 plant species and 351 fragrance compounds emitted by them.

Dr Dyer said the process was extremely complex, involving "multisensory information transfer" between the plant and the bees.

Old behaviour, new understanding

Dr Dyer said the ancient Greek philosopher Aristotle noticed more than 2,000 years ago that a bee from one hive would go to the same type of flower every time, while its sister bee from the same hive would go to a different flower, also sticking to that colour every time.

He likened this practise to the way humans became used to a particular food and automatically went back to it every time.

The researchers believe the purpose of this system is to ensure that individual bees stick to one type of plant and avoid "pollen clogging".

"For example, if plant species A gets pollen from plant species D, it could clog the reproductive parts of the flower and prevent reproduction," Dr Dyer said.

"We need a fair bit of fidelity in plant systems for them to persist in a fairly robust way."

He said plants that used wind pollination did not require this selective approach, but for plants relying on bees, it was crucial.

"They need the bee to go the same flower over and over and over," he said.

When is a smell not a smell?

They key to understanding how complex these signals are is to realise bees do not perceive fragrances like humans do.

"It's difficult to describe how an insect perceives a scent compared to how we see it," Dr Dyer said.

"It's really a profile of a whole heap of compounds, so it doesn't translate into an easy term we can use.

"What we can tell by looking at the components of the scent signals is that they are very closely related to plants which have the same flower colourations, despite being different plant families.

"That level of complexity, we did not know existed in nature."

The researchers said the finding could be put to use in agriculture, where pollination is vital and concern is growing about the bee populations and the balance between different bee species.